The present invention relates generally to a cryogenic support member and more particularly to a cryogenic support member which comprises a fiber reinforced plastic (FRP) tube with metallic end connections.
Conceptual design for a proton-proton collider, called the Superconducting Super Collider (SSC) are underway. The proposed particle collider for high energy physics research will employ superconducting accelerator rings. The SSC incorporates two adjacent 32 km diameter accelerator rings in a common tunnel. The rings consist of dipole magnets for bending, quadrupole magnets for focusing and special magnets for correction. The ring magnets must provide the specified magnetic function, have low refrigeration load, operate with very high reliability and be manufacturable at a low cost.
The cryostat features are critical to the SSC design. The cryostat must function reliably during transit, transient, steady-state and upset operating conditions. The major components of the cryostat are the cold mass assembly, thermal shields, insulation, vacuum vessel, interconnections and the suspension system.
The magnet suspension system functions under a variety of conditions which include assembly, shipping and installation, cooldown and warmup, steady-state operation and upset conditions. The suspension system must have the attributes of low cost; installation and adjustment ease; high reliability; positional stability; and low heat leak.
The cold mass assembly and shield assemblies with their distributed static and dynamic loads are supported relative to the vacuum vessel at several points. The number and location of these important points is determined by the beam deflection of the cold mass assembly and the need to optimize the number of support points for reasons of fabrication ease and low heat leak. The suspension system will employ several post-type supports and an independent anchor at cryostat mid-length for axial motion restraint.
The SSC refrigeration requirements are very stringent and result in low heat leak budgets. The heat leak contribution of the suspension system must be minimized to optimize cryostat design.
The use of the tubes or columns of fiberglass/epoxy to support superconducting magnets and other cryogenic objects is well established technology. Fiberglass/epoxy material, commercially designated as G-10 or G-11, has a very low thermal conductivity and has good compressive and tensile strength at low temperatures. In this respect, U.S. Pat. No. 4,325,530, entitled "Cryogenic Structural Support", illustrates the use of a FRP laminate in a structural support member in tension.
It is desirable to have some means for securing the support member to the magnet system at one end and to a foundation at the other end of the support member. Typically, this is achieved by attaching a metallic end connection to the ends of the FRP tube. The metallic end connections can then be fastened, bolted, welded, or chemically bonded to the magnet system or the foundation. Illustrative of this design is the support member shown by Timmerhaus et al., "ADVANCES OF CRYOGENIC ENGINEERING", Proc. International Cryogenic Materials Conf., 2nd Vol. 24, using a bolted connection.
The prior art, however, fails to disclose a method of joining the FRP tube to the metallic end connections which will withstand the repeated mechanical and thermal stresses imposed on the support member by a system such as the SSC. The method which have been heretofore used to join the FRP tube to the metallic end connections have severe limitations. The use of epoxy bonding to join the two materials leads to a joint which may crack upon thermal or mechanical cycling. The use of screws or bolts to fasten the metallic connection to the FRP tube leads to penetrations in the FRP tube. Such penetrations can cause the failure of the tube upon repeated load cycling. The use of the threaded connections to join the metallic connection to the FRP tube also produces a poor joint. The threads in the FRP tube can fail with repeated load cycling. The present invention overcomes the failings of the teachings of the prior art by using a metallic end connection which is shrink-fitted to an FRP tube. The present invention thus, avoids the problem of epoxy bonding which could crack upon thermal cycling. The joint is non-invasive and the FRP material strength is not reduced by pentrations, threads, etc. The thermal interference joint produced by the shrink-fitting the metallic and FRP components is good in tension, compression and bending. The joint also generates excellent thermal contact between the materials and, thus, produces a very good heat intercept.
Shrink-fit techniques have heretofore been used in a variety of applications. U.S. Pat. No. 1,735,563, entitled "Method of Securing Metal End Couplings On Tubular Members", discloses a method of securing metal end couplings to a metal tube. A plug is shrink-fitted inside of the tube and metallic coupling. This patent, however, illustrates the distrust in the prior art in the strength of a shrink-fitted connection, as the component parts are forged, welded, or fused together in addition to the shrink-fitted connection. Further, this patent discloses only a method of joining two metallic parts. This patent does not address the problem of fatigue or creep effects which may come into play when an FRP or other non-metallic material is used. Creep effects in an FRP composites and laminates may pose a problem for an FRP member in compression or tension. Creep analysis have been performed by Foye, "Creep Analysis of Laminates Composite Reliablility", ASTM STP 580, American Society for Testing and Materials, 1975, pp. 381-395 and by Markley et al., "Energy Saver Cryostat Support Material Creep Measurements", 1984. It has been heretofore believed that creep effects would cause an FRP tube pinched between two metallic components to extrude out of the joint area.
U.S. Pat. No. 4,499,646 discloses a technique for joining a metallic shaft to a ceramic shaft using an expansion sleeve. An expansion sleeve is placed over a ceramic shaft and both parts are inserted into the hollow part of a metallic shaft. The end of the ceramic shaft is threaded and mated to the metal shaft. Upon heating, the expansion sleeve expands, further securing the ceramic shaft to the metallic shaft. This technique would be inoperative in the support member of the present invention, as the expansion sleeve functions only at elevated or heated temperatures. The support member of the present invention will operate below elevated temperatures.
The prior art discloses the use of shrink-fit techniques to join FRP material to metallic tubes. U.S. Pat. No. 3,731,367, entitled "Method of Assembling Compound Body", discloses that a metal tube may be cooled and inserted into an FRP tube and upon expansion of the metal tube, by subsequent heating to room temperature, the metal tube and the FRP tube are securely bonded together. This technique would be inoperative for the present invention. While this technique forms a strong compound body, subjecting the two members to loads applied in different directions would lead to a failure of the joints between the FRP tube and the metal tube. Thus, this connection would produce a poor metallic end connection for a support member, as the metallic end and FRP components will be subjected to forces acting in opposite directions. Additionally, cooling the compound body to cryogenic temperatures would lead to a weakened joint between the two tubes.
Shrink-fit processes have been used in a variety of other applications as exemplified by U.S. Pat. No. 4,074,412, entitled "Method of Repairing or Reinforceing Tubular Plastic Members"; U.S. Pat. No. 4,470,415, entitled "Sutureless Vascular Anastomosis Means and Method"; and U.S. Pat. No. 4,169,477, entitled "Anastomatic Couplings". These patents, however, do not disclose a joint which will be strong in compression, tension, and bending, nor do these patents disclose a joint which will be operative at cryogenic temperatures.
The joints of the cryogenic support member of the present invention generate excellent thermal contact between the materials and, thus, may be used as a very effective heat intercept. The use of heat intercepts in a cryogenic support member is illustrated in U.S. Pat. No. 4,325,530 and by Timmerhaus, et al., cited above. The heat intercepts utilized in the above devices either are epoxied to the FRP tube or are inserted between plies of laminate of the FRP. These methods of joining the heat intercept to the FRP member yields a heat intercept with a low thermal efficiency.
Therefore, in view of the above, it is an object of the present invention to provide a cryogenic support member which has a non-metallic member for support and metallic end connections.
It is another object of the present invention to provide a cryogenic support member wherein the coupling between the non-metallic member and the metallic end connection is good in tension, compression and flexure well above, and well below the temperature at which the coupling was assembled.
It is still another object of the present invention to provide a cryogenic support member in which a non-metallic member is not weakened by penetrations.
It is still another object of the present invention to provide a cryogenic support member wherein the non-metallic member is fiber reinforced plastic.
It is yet another object of the present invention to provide a cryogenic support member which has efficient heat intercepts.
Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.